Translucent and semi-gloss films are widely used in industry. There are different ways to obtain the desired properties in such films. For example, a film can be made semi-gloss by casting the film to a matte surface. Various additives with different refractive indices can be added to prepare films having reduced transparency or to prepare films having a translucent appearance. For extruded polyester films, additives such as silicon oxide and titanium oxide are widely used in the extrusion process to obtain translucent or white films. Coating or co-extruding a skin layer is known to enhance the semi-gloss properties over the translucent properties of a film. Additionally, it is known to utilize incompatibility between the additives and polyethylene terephthalate (PET) to create voids to prepare white film. In many cases, highly incompatible organic polymer particles such as polymethylpentane are added to produce translucency in a film.
Talc and other layered inorganic materials have been used in the plastics industry due to the ability of these materials to increase dimensional stability, flexural modulus, and impart improvement in heat distortion temperature. For polypropylene film, these materials have been used as antiblocking and/or nucleation agents. Talc has also been combined with polyurethane to facilitate crystallization of a polyurethane composition, particularly a polyester-based polyurethane composition. For example, U.S. Pat. No. 6,458,880 discloses a polyurethane composition containing polyurethane (e.g., a polyester-based polyurethane) and sufficient talc to provide a crystallization temperature of the polyurethane composition that is at least 10° C. greater than the crystallization temperature of the polyurethane composition without talc. The addition of talc can enable rapid formation of products, by for example, injection molding, compression molding, extrusion, and film formation techniques. Talc has also been used in flame retardant films as an effective material for preventing dripping such as in U.S. Pat. No. 6,174,943. The disclosures of the foregoing are incorporated herein by reference in their entirety.
Generally, talc is known to have a moderate adhesion to polyester. Further, biaxially oriented polyester films which contain talc particles are typically opaque because the incompatibility between the talc particles and polyester creates micro-voids around the particles after orientation. Accordingly, such matte films typically posses a relatively high haze number. Reducing the amount of talc in the film may reduce the amount of haze, but also increases the gloss of the matte image.